This invention relates to a vertical shaft system ensuring the vertical alignment of the pendulum system of gyroscopic theodolites with two degrees of freedom for azimuth determination.
The bearing of the vertical shaft of the pendulum system of gyroscopic theodolites used for azimuth determination is selected as to obtain possibly a minimal moment of friction in relation to the directional torque of the gyroscope.
There are such frictionless shafts, where the azimuth determining pendulum system is suspended on a wire and in this case the shaft is formed by the torsion pendulum itself. Since the nearly horizontal axis of the gyroscope--partly depending on the latitude and partly owing to the rotation of the pendulum system around the vertical shaft--is compelled to move in the vertical plane too, thus this degree of freedom is restricted only partially by the above described pendulum system. In these systems the period of oscillation around the vertical shaft of the gyroscope with nearly horizontal axis is relatively long. The period of oscillation can be reduced by increasing the length of the pendulum, which is difficult for constructional reasons i.e. large dimensions, weight. In the case of given gyroscopes the period of oscillation will be the shortest when the pendulum system comprising the gyroscope has two degrees of freedom, i.e. the gyroscope is capable of turning only around its own axis and around the vertical shaft.
The known sliding-, ball-, gas-, magnetic-bearings may be used for supporting said vertical shaft. Since the maximum value of the so-called directional torque is only a few 100th Nm, in case of gyroscopes used for azimuth determination only such solutions may come into consideration, where the moment of friction is as low as possible.
The moment of friction of the miniature ball-bearings having a small friction coefficient is so high that they are suitable only for the shaft of the pendulum system of an instrument with low measuring accuracy. The disadvantage of the magnetic bearings is that owing to the unavoidable impurities present in the pendulum system, under the influence of the magnetic anomalies, directional torque will be produced.
Use of the gas-bearings is complicated and costly, because perfectly smooth bearing surfaces have to be formed, furthermore under varying bearing load the air gap has to be kept a constant value, consequently the gas supply is to be provided with automatic control system varying the pressure or the rate of feed.